Influence of Dissolved Organic Carbon, pH, and Microbial Respiration Rates on Mercury Methylation and Demethylation in Lake Water

Abstract

Effects of changes in DOC concentrations, pH, and microbial respiration rates on specific rates of mercury methylation and demethylation in lake water were studied using radioisotopic techniques. Increased concentrations of DOC resulted in decreased specific rates of net methylation, possibly as a result of complexation of inorganic mercury with DOC. A reduction in pH from 7.0 to 5.0 had the greatest effect, causing large to moderate increases in net methylation rate at both low and high DOC concentrations (500–2600 μM). Rates of respiration (indicative of general rates of microbial activity), which were insensitive to pH change over the range tested (5.0–7.0), had the smallest effect on net methyl mercury production rates. We propose the following explanations for three situations in which high mercury concentrations are commonly found in fish. (1) in acidified dilute clear-water lakes, high fish mercury concentrations may be a result of enhanced in-lake methylation; (2) in brown-water circumneutral lakes, where in-lake methylation is inhibited by high DOC concentrations, terrestrial inputs of methyl mercury may be most important; and (3) in brown-water, low-pH lakes, both in-lake and terrestrial sources of methyl mercury may contribute to elevated mercury concentrations in fish.

The Bioaccumulation and Migration of Inorganic Mercury and Methylmercury in the Rice Plants

“…The alteration of soil properties could have an important effect on MeHg production, which could cause the different concentrations of soil MeHg. For instance, soil organic matter could increase MeHg production [23] or inhibit the process of Hg methylation by binding strongly with IHg [24]. Also, it has been reported that clay could bind the IHg itself or form clay-OM to adsorb IHg [25], which could result in the decrease of bioavailable IHg in soil, thus inhibiting the production of MeHg.…”

Sulfur in the South Florida Ecosystem: Distribution, Sources, Biogeochemistry, Impacts, and Management for Restoration

“…These may include inorganic mercury inputs and bioavailability, redox conditions, pH, and dissolved organic carbon (Aiken et al, 2011;Miskimmin et al, 1992). All of these factors, especially the high rate of mercury deposition in south Florida, are factors in the high levels of MeHg production and bioaccumulation in the Everglades (Gilmour et al, 1998(Gilmour et al, , 2007a.…”

Geochemical and Biological Controls over Methylmercury Production and Degradation in Aquatic Ecosystems

“…74,86) cover thespectitiOn ofHg 10 the presence of sulfide but it is known that Hg binds strongly to (jrganic rnatter~and that dissolved organic carbon (DOC) impacts Hg methylation. The impact of organic content on Hg metbylatic)8 appears to be comple;K (16,57,58 suggests lhat a decrease in pH will lead to a decrew;c in methylation rate in sediments because of changes in the concentration of bioavailab1e Hg in porewaters. The magnitude of the effect will depend on the pH range 8$!he impact of pH is more marked at low pH.…”